Geomorphic and Sedimentological Impact of the 2017 Flash Flood Event in the City of Comodoro Rivadavia (Central Patagonia, Argentina)

Abstract

From March 29 to April 08, 2017, the city of Comodoro Rivadavia (Chubut province, central Patagonia) had experienced the worst floods due to rainfalls that reached up to 399.4 mm. This study investigates the response of channel reaches in a semiarid environment, analyzing the range of erosional and depositional processes observed in ungauged catchments. Seven ephemeral riverscover approximately 1546 km2 and are characterized by high slopes, that favored high runoff velocity and gully development during the storm. Heavy rains generated intense rain splash erosion and overland flow, providing high-concentration of suspended particles to the streams, with the additional incorporation of pebblesized clastic components associated with natural and anthropogenic sources. Due to unusual discharges, aggradation and widening of the channels occurred in the higher-order streams, flooding large urban areas. Medium to fine sand-sized, transient deltas up to 500 m of radius were built in the coastal zone during the storm. The extreme rainfall event revealed a lack of planning at the catchment scale. It is reflected in a substantial reduction of the plant cover, anthropogenically-induced changes in channel shape and route of sediments, urban development in low and flat zones with flooding risk, and under-sized human-made waterways within the city.